Oceans & Coastal Resources:
A Briefing Book
Congressional Research Service Report 97-588 ENR
Redistributed as a service of the National Library for the Environment

Coastal Flooding, Erosion, and Sea Level Rise

Prepared by Jeffrey A. Zinn

Senior Analyst in Natural Resources Policy
Environment and Natural Resources Policy Division

Issue Definition
Background and Analysis
Status of the Issue
Continuing Concerns
Sources and References for Further Information

Issue Definition

Changing water elevations and storms modify the coastal environment; generally, the larger the change or the storm, the greater the modification. These physical processes make the coast highly dynamic. Efforts to stabilize it at one location often exacerbate problems at adjoining locations. Stabilization efforts are substantial because property values are very high along the immediate coast and because owners seek to stabilize the shoreline and protect their investments. Trying to stabilize the coast is very expensive and usually provides an illusory and temporary solution. At issue is the appropriate role of the federal government, given both the high cost of stabilization efforts and the high likelihood for continued change, which will grow with any rise in sea level.

Background and Analysis

Hurricanes and other coastal storms have caused billions of dollars in damages, especially along the southeastern coast of the United States. These storms strike periodically and randomly. As more development is concentrated along the coast, smaller or less intense storms cause more extensive and expensive damage. Also, if sea level rise occurs, then smaller and less intense storms will cause more damage because they will be starting from a higher water elevation. A main cause of damage is coastal flooding, and one of the most serious forms of damage is coast erosion.

Coastal flooding is addressed through the National Flood Insurance Program. This program makes flood insurance available in return for local government taking actions through building codes and planning that are intended to reduce future costs, in lives and property damage, of major storm events. The flood insurance program has been less than fully successful, often because local governments have not vigorously enforced the development controls needed to make it succeed. When the 103rd Congress amended the program, it directed the Federal Emergency Management Agency to study specified aspects of coastal erosion, but there has been no follow-on activity.

While the flood insurance program was intended to address coastal erosion, experts have never agreed on methodology that would allow them to predict the future rates and patterns precisely enough for insurance purposes. Past erosion rates do not necessarily continue, and patterns change with the configuration and profile of beaches. Rates of change are highest during rare severe storm events. Therefore, over the useful life of a structure, say a house, there might be only a couple of severe erosion events.

The federal government addresses coastal flooding, coastal erosion, and potential sea level rise through the Coastal Barrier Resources Act of 1982, but only on designated undeveloped coastal sites. Designated sites, by definition, are generally where there is limited pressure to protect the shoreline as it exists today.

Potential sea level rise, unlike erosion and flooding, is not addressed in federal programs. Many experts predict that the sea level will rise significantly over the next century as a result of global warming, although projected rates and the total amount of change are subject to considerable debate. Such changes could vary from place to place, depending on the pattern of development and the profile of the shoreline. For example, a study of coastal Massachusetts, using predictions that sea level could rise by between .45 feet and 1.57 feet by the year 2025, concluded that the state would lose between 3,000 and 10,000 acres with property value losses of between $3 and $10 billion. Political leaders may find it hard to address a problem involving major uncertainties when its impacts would be far into the future, and when technical experts cannot agree on how to characterize the problem.

Low, flat jurisdictions would be subject to the greatest risks, and no area is considered to be more at risk than coastal Louisiana. Louisiana is losing an estimated 60 square miles of coastal wetlands a year to coastal erosion, and if the current pattern continues, much of three parishes could disappear in the next century. The problems in Louisiana are attributed to a combination of changing natural conditions and human actions that would be exacerbated by any sea level rise. Some of the man-induced causes are being addressed, most notably the dredging of channels through the marshes to provide oil rigs with access to drilling sites. But other factors, such as the loss of sediment caught behind dams upstream on the Mississippi River and its tributaries, are more difficult to address. In addition, much of the Mississippi delta, which is unconsolidated sediment, is sinking under its own weight.

Solutions to these hazards fall into three categories. One is to retreat from the beach, implementing proactive policies to move future development inland to a point where it is not threatened by anticipated water elevations. Some coastal geologists and environmentalists support this approach because it would spare today's coast from more development, allow natural processes to continue, and reduce the loss of property and lives when a storm strikes. The second and third are to barricade the beach and to build up the land. These are favored by shorefront property owners and many in the development and engineering businesses. But the barricade-the-beach approach cannot succeed unless an entire beach system is included, and building up the land may only work so long as the ocean does not go around it. There is much debate not only on the relative feasibility of these options, but also on costs of each in both the short and long terms. Congressional debate comparing and contrasting these approaches is likely to continue so long as sea level rise is seen as a possible problem.

Status of the Issue

There is a great deal of uncertainty surrounding some aspects of this issue, and some very specific and immediate needs in other aspects. Consequently, Congress has addressed a few of the specifics, such as loss of wetlands in Louisiana, but it has not addressed the full issue. At the same time, several states, through coastal management and other programs, have started to examine these problems and seek solutions as well.

Congress must decide whether it should act now, when there is still considerable controversy and uncertainty among scientists about the probable rate and pattern of sea level rise in the future. A second issue is the related debate over whether some solutions to erosion that are currently used, most notably beach nourishment projects, are cost effective over the longer run. If Congress decides to attempt to stabilize portions of the coast, it will also have to determine how to fund this expensive effort.

Continuing Concerns

These concerns and questions are provided to stimulate further discussion of the issues noted above.

  1. What options, structural and non-structural, are available to the federal government to protect life and property in coastal areas from flooding, erosion, and potential sea level rise? What are the limitations and opportunities associated with each option? How does the tight federal budget situation affect the selection of options?
  2. Recognizing that sea level rise may have an impact at some time in the future, but the rate and extent of the rise are unknown, what could the federal government do now to anticipate the kinds of problems that would accompany sea level rise? What, if anything, should it do?

Sources and References for Further Information

National Research Council, Committee on Beach Nourishment and Protection. Beach Nourishment and Protection. Washington, DC: National Academy Press, 1995. 334 p.

National Research Council, Committee on Coastal Erosion Zone Management Managing Coastal Erosion. Washington, DC: National Academy Press, 1990. 182 p.

National Research Council, Committee on Engineering Implications of Changes in Relative Mean Sea Level. Responding to Changes in Sea Level: Engineering Implications. Washington, DC: National Academy Press, 1987. 148 p.

U.S Congress, Office of Technology Assessment. Preparing for an Uncertain Climate--Vol.I and Vol II. OTA-O-568. Washington, DC: U.S. Govt. Print. Office, 1993. 63 p. and 383 p.

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